Could easily be the alternator belt. They're very good at squealing when the
alternator is delivering a high charge, like when headlights, wipers and heater
fan (and maybe rear demister) are on when you first start off.

Sounds to me like the infamous 300Tdi fan belt squeal.  There are various
so called cures but it will most likely persist.  Strangely enough mines
been quiet for some time now.

You could try changing the belt tensioner pulley bearing as it may be worn
and putting the pulley out of alignment.  Others have suggested changing the
belt for a known good brand one.  Some people have had success by using
some emery and removing the glaze from the tensioner pulley.

I just ignored mine and like I say it's been quiet for a while.  After
driving a ford it makes the odd chirping noise but soon shuts up.

Possibly the serpentine belt or the the bearing in tensioner.  

Steve. Suffolk.
remove 'knujon' to e-mail

Squirt some water on the alternator belt. If the squeak goes
away, you've found the source. Then do a Google to try some of
the very many "cures"!

A technician at a fan belt manufacturers suggested it was glaze
on the belt and tensioner pulley. The effect is the same as
drawing your finger down a damp window -- or chalk on the school
black board.

Can be removed by glueing some emery paper to small piece of
wood and rubbing the tensioner pulley with the engine running.
Also a good way to lose a finger or two.

Derry

Thanks all, it seems I am in for many squeaks as they are predicting the
hardest winter this century !!